If you want to use a specific weapon or character, wait for a Steam sale. Payday 2 DLCs regularly go on sale for pennies.
This is where many players get confused. many popular hack features, including: payday 2 how to know if you have a cheater tag top
Identify the item causing the flag (usually a DLC item or skin you don't actually own). Unequip the offending item from your loadout. If you want to use a specific weapon