What is the ruling on financial transaction obsessive thoughts (waswasah), and what should I do about not having signed for the prices of medicine I purchased from the pharmacy after the pharmacy sent the prescription to the institution?

There is no justification for worry or confusion, and nothing is incumbent upon you regarding what you mentioned. It is advisable not to surrender to obsessive whispers (waswas) or to excessively exercise caution and doubt, in order to avoid their increase. Actions should be built upon the principle of safety and the presumption of innocence, and one should not burden oneself with what it cannot bear, nor be excessively strict in matters that do not necessitate it. Seek help from Allah and frequently engage in His remembrance and supplication.