. . . . Paid for and downloaded encoder for MOV. Activation code does not work. . . . .
Which version of Movie Edit Pro (MEP) are you running and what is your computer specification - see this topic for details required and please quote the processor and graphics card/chipset make/model in full.
It would help for future reference if you put this information in your profile signature.
Where from and what is the full name name of the 'encoder' you purchased, or do you mean 'codec' as in the HEVC codec which has a fee based activation to enable import/export (decoding/encoding) of HEVC video?