Manufacture: the manufacture of medicines requires a licence in accordance with § 13 of the Medicines Act (AMG)
Marketing: this requires a licence in accordance with § 1 clause 2 of the Pharmacists Act (ApothekenG).
Wholesale: the wholesale of medicines requires a licence in accordance with § 52a of the Medicines Act (AMG)
Expertise is necessary for the retail sale of OTC medicines , § 50 A of the Medicine Act (AMG)
Responsible body: Chamber of Commerce (for the retail sale of OTC medicines).

You will need an itinerant trade licence for itinerant sales, e.g. at private flea markets and other non-fixed events.

You will need a catering licence is you sell goods in private areas, e.g. on a supermarket car park. Following amendment of the Catering Act, a catering licence is no longer required unless alcohol is served.
No licence is required for sales at fixed markets, e.g. weekly markets, annual markets.
Responsible body: Consumer Protection Agency OR The Point of Single Contact in Hamburg