The manual is here:
https://midsummerwholesale.co.uk/pdfs/en-k-manual-v1.4.pdf
appears that the 13mm size refers to the outer diameter of the round cable that can be used with the AC connection plug but has been jumbled up with other information. Page 17 onwards.
A 100A breaker will be of no use - plenty of homes have an incoming supply smaller than that.
If that flat cable has been shoehorned into the inverter connection plug, it's the wrong type.
May not be secured properly.
Round cable is required.