no start, constant clicking, batt seems OK

[Roadrally]

As many others say, fully charge the battery first, if it doesn't hold charge then change it but ensure the bsi is in sleep mode (if you search then there is a full description of how to remove and refit a battery safely)
If you try to jump start Peugeot/Citroen then you can spike the bsi.
Earth straps are also a weak point, remove and clean up both ring terminals that are on the gearbox an the chassis.