What is the ruling on the financial percentage I receive in exchange for purchasing invoices for my company to cover its expenses, knowing that these invoices are valid and their taxes have been paid?

If taxes are permissible and justly levied, then it is not allowed to evade them. However, if taxes are oppressive and unjust, there is no harm in evading them to the best of one's ability, even if that involves purchasing fictitious invoices, provided that one does not expose oneself to humiliation and harm. This is based on the Prophet’s (peace be upon him) saying: "It is not befitting for a believer to humble himself." The ruling on the percentage given due to this evasion follows the ruling of the taxes themselves.