How to fix capillary action on anti-condensation coating on box profile steel roofing sheets?
PREPARATION &amp; FITTING INSTRUCTIONS FOR ANTI-CONDENSATION ROOFING SHEETS
INSTALLATION
Note! This product is designed for use on roofs with a pitch of 10 degrees or greater.

And that's pretty typical of all steel roofs, and yours is the reason why.
The only way you can make a steel roof work on installations like this is if one piece of metal can span the entire roof.  Not half to a peak. (because you can't make the peak seam work either, same reason).  You can't have seams.
The simple fact is, you have a flat roof.  1-3 degrees is pretty much the minimum slope required to keep a flat roof from becoming a swimming pool, and is required by most roofing systems.  You need to use products appropriate to flat roofs, such as EPDM rubber.