The "official" digital credential, developed some years back by the Pilgrim Office, never did catch on. I do not think it is being supported anymore.
In view of this,
I strongly recommend that ALL pilgrims use sellos / stamps in a paper credencial to document their journey to Santiago, regardless of the actual route taken.
Many pilgrims start on the Frances, then cut to the Invierno to avoid the Sarria section. It is a day or two longer, but really pretty.
The office staff is used to seeing this detour / variation in credentials. Just point it out when you arrive. Essentially, you walked the
Camino Frances, but via the Invierno at Ponferrada.
Apps, like the Wise apps, will provide excellent coverage for both the
Camino Frances, from your starting point to Ponferrada, and the Invierno app from Ponferrada to Santiago.
Personally, I would use two apps on my iPhone, and one paper credencial to plan, and then document my Camino along the OPs planned route.
It will all sort out.
Hope this helps.
Tom