Difficulty to see presence of offline maps

I continue to try to help a colleague with Locus Map Pro via 'phone and email. He downloaded Madeira from OpenAndroMaps, extracted the .zip file to his PC and copied Madeira.map to Locus>mapsVector on the internal storage of his Asus MeMO Pad 8 Android tablet. The file was seen immediately in the Maps page. We have had no success with further maps subsequently. He followed the same process with Great Britain and, just to use a small file, the Canary Islands. Neither shows, but Madeira continues to do so. He has tried 'Refresh list', exited and reopened Locus Map Pro, and powered off and on his tablet. All to no avail.

I asked him to create the same folder structure of Locus>mapsVector on his microSD card and move Canary Islands there. Nothing displayed having carried out the various attempts above.

Nothing was achieved in Locus Map on his wife's 'phone, either.

I asked him to create a new folder, 'Maps', in Locus folder and alongside mapsVector. He moved Canary Islands there. He went to 'External maps' on the Maps page and located the required .map file. He received a message, "Selected path is not allowed."*

I have no personal experience of difficulties with multiple .map files on my own 'phone. I do not expect this to be a Locus Map problem but I am at a loss now to know what further to advise. His Locus Map version is 3.28.0.

Edit:

* I see from my 'phone's file manager that 'maps' folder within Locus folder exists already. I did not know know of its existence until now (back to the Windows File Explorer issue of previous posts!). What is its purpose compared with 'mapsVector'?

Reading the Knowledge Base now, I understand the 'External maps' facility is for such as an SD card. This is why the message appeared, perhaps, because the attempt was to access internal storage?