Is the manager liable for 50% of the loss if profits and losses are divided 50/50 between him and the shop owner?

The contract between the questioner and the shop owner is either a lease contract or a Mudarabah (profit-sharing) contract:

If it is a lease contract for a salary and a percentage of the profits, the majority of scholars hold that it is impermissible due to the ambiguity of the wage, but some have allowed it. In this case, the employee's share of the profits is only realized after compensating for any losses; thus, the employee receives their full salary but loses their agreed-upon percentage.

If it is a Mudarabah contract, it is not permissible in Islamic law for two reasons: 1. Mudarabah can only be in cash or in goods valued in cash. 2. It is not permissible for Mudarabah to be based on a specific amount, with or without a common percentage, as stipulating a known sum of money invalidates the partnership.