What is the ruling of the Shari'ah on issuing fictitious receipts to cover a deficit in an advance payment resulting from sales taxes, or to help a worker who has no rights, and would I incur sin by signing them?

The fundamental principle governing the relationship between financial management and other departments is clarity and honesty. Regarding the financial advance allocated for building maintenance, it must be disbursed for its designated purpose. If the financial management does not approve the sales tax necessary for your work, then there is no harm in writing its receipts under other designations, such as petty cash, because the advance is paid for this purpose, and the tax is part of it. However, using the advance for purposes other than what it was allocated for is not permissible for the manager or anyone else, because it is not their property. Whoever does so is liable, as the Prophet (peace and blessings be upon him) said: "The hand is responsible for what it takes until it returns it."