Since no one else answered...

Payment Entity means, any Governmental Authority or Person, in its capacity as employer (or the relevant labor union of the employees of such Governmental Authority or entity, as employer) which has the obligation to pay salaries or pensions to the borrowers of the Loans, as applicable, and which has entered into a Collaboration Agreement with the Company or its Subsidiaries. http://www.lawinsider.com/dictionary/payment-entity

The "P" is known (pago or payment), and Asker has reason to believe the abbreviations stands for English words.

So we just need to confirm that "Sujeto" can be construed to mean "Entity."

sujeto social loc nom m (sociología: ser humano) social entity, social being n
Marx tenía muchas teorías sobre el sujeto social.
Marx had many theories about the social entity (or: being). (Found on wordreference.com)

sujeto pasivo

1. m. Der. Parte obligada en una relación jurídica.

2. m. Der. En materia de tributos, persona obligada a su pago según la ley.
(Found in the rae.es online dictionary of Spanish language)

So we have a least some evidence that "entity" can be used to translate "sujeto." We also have at least some evidence that "sujeto" can have a connotation of one who is obligated to pay something.

Although Payment Entity seems to be the best fit for what you are working on, since I have limited context I also want to point out that there are at least two other meanings of PE in finance/accounting/business: price-to-earnings ratio and private equity.