The USSR reconstructed Poland after the war, and often forgave Polish debts. From @AnarchoBolshevik@lemmygrad.ml's research:

Quoting Dorothy W. Douglas’s Transitional Economic Systems: The Polish–Czech Example (a work by an economic anthropologist), page 66:

In foreign trade the pre-war level had now been surpassed,² and on a per capita basis it was two-thirds above pre-war. A trade agreement concluded with the Soviet Union early in 1948 had ensured the importation of investment goods to the value of £112,000,000. In general, trade with the Soviet Union had risen from 0.4 per cent in 1938 to 21.5 per cent in 1948; and trade with her and the other countries of planned economy now accounted for over a third (37.8 per cent) of [the Polish People’s Republic’s] total foreign trade.

Page 130:

Much the largest piece of industrial construction listed for the Six-Year Plan was the great steel combine of Nowa Huta (‘New Foundry’), near Cracow. Deliberately planted in the most poverty-stricken and probably the most traditional-minded province in Poland, a region of dwarf farms, the new ‘socialist city’ when completed was to house 100,000 persons.³

Another characteristic note was that the entire equipment of the foundry and its related works had been furnished out of the proceeds of the 1948 long-time investment loan granted Poland by the Soviet Union, and that all the major parts were actual imports from the Soviet Union, complete with all their technical documentation.

Pages 310–311:

The Polish–Soviet Trade and Investment Agreement of January 1948 referred to above by the Economic Commission for Europe, was stressed in after years by the Poles as a landmark in their industrial history. Besides providing for the exchange of goods, it extended to [the Polish People’s Republic] credits for great amounts of industrial equipment to be sent during 1948–56. Payment was to be over a period of ten years, chiefly in goods, at 3 per cent interest.

This credit, the Poles later stressed, was the largest that Poland had ever received. The investment credit amounted to some £112,000,000, and enabled [the Polish People’s Republic] to start carrying out her Six-Year Plan in more than thirty industrial branches. The investment goods were destined for plants of both heavy and light industry.

In heavy industry the Poles made much of the new steel plant of Nowa Huta that, when completed, was to double the country’s existing steel capacity: they pointed out that it was wholly Soviet financed and was built mainly on Soviet deliveries.

The next most important items were several large chemical factories. Pre-war Poland had had no chemical industry. In light industry the Poles made a dramatic showing of the Soviet Union's contribution in 1951 by having a series of plants in different parts of the country start production within a few days of each other close to 7 November.

These included a factory producing the first passenger motor-car in Poland, a new lorry factory, a new textile factory, and a large transporter for the mechanical loading of ships. Ail of these, the press emphasized at the time, had been not only Soviet financed, but had been erected on the basis of Soviet plans and machines and with the aid of Soviet specialists.

In 1950 [the Polish People’s Republic] received further increase of credit from the Soviet Union. By the close of 1951 not all of this had as yet been used. The new agreement to run from 1953–8 provided that nearly 40 per cent of all Soviet exports to [the PPR] would be capital goods.

The Council for Mutual Economic Assistance

For the smaller planned economies plainly a double process had been at work. From the Soviet Union came major investment credits, technical equipment and industrial raw materials, as well as, especially in times of stress, grains and feeding stuffs.

Page 359:

Assistance from Soviet specialists was used. And technical delegations of all sorts from the two countries visited the Soviet Union. The Polish Government, stated President Bierut at the end of 1950, in discussing innovations under the Six-Year Plan, had asked for and received the services for several months of groups of Soviet specialists.

‘The Soviet specialists made an analysis of our Plan in those branches which are of foremost importance to us: coal, metallurgy, machinery, chemicals, and power; they gave exceptionally valuable advice to our engineers and industrial managers; they corrected individual mistakes and made important suggestions. […]’

He added, significantly enough, a note on personal contacts: ‘In the course of exchange of professional views and experience. […] Polish engineers and industrial managers […] were thus able to become acquainted with the talents, science, and style of work of a new intelligentsia. […]’¹

Several different notes were struck in regard to the interdependent progress of the planned economies. Emphasis was laid, as above, upon Soviet aid.

Quoting Sultan Barakat’s Russia's Approach to Post-Conflict Reconstruction: The History, Context, and its effect on Ukraine, page 40:

And, “[immediately] after the end of the war, the USSR transferred 15% of the German reparation payments to Poland. The amount was equal to the U.S. assistance to France under the Marshall Plan” (Zatsarin, 2016).

The Soviets also forgave Polish debts. Quoting Adam Zwass’s The Council for Mutual Economic Assistance: The Thorny Path from Political to Economic Integration, page 22:

Khrushchev […] stopped deliveries at prices which were not always able to cover the costs of transport (between 1945 and 1954 Poland delivered 50 million tons of coal at a price of 1.28 U.S. dollars per ton, which was only one-tenth of the price [that] it could have had on the world market). Khrushchev was willing to write off a portion of the credits granted from the books as repayment for the damage caused, including 3.2 billion złotys and 22.3 million U.S. dollars of Poland’s debt.