Help with instant boost from One Retainer's Journey IV

[Anomini]

Yep! I set the base job to Thaumaturge and I put weathered scepter on retainer.

Then I clicked on "Increase Retainer Level (lv 90) Item Required: One Retainer's Journey IV" and it says "You can only advance your retainer as far as level 21 to match your current level. Do you wish to proceed?" I can't see anything to change retainer class to Red Mage and I was on as rdm too.

Since I boosted my character to 90 rdm, no ventures and no levels on GC. So nothing for the advertised instant boost to level 90 rdm, still. :/

[CVXIV]

Yep! I set the base job to Thaumaturge and I put weathered scepter on retainer.

Then I clicked on "Increase Retainer Level (lv 90) Item Required: One Retainer's Journey IV" and it says "You can only advance your retainer as far as level 21 to match your current level. Do you wish to proceed?" I can't see anything to change retainer class to Red Mage and I was on as rdm too.

Since I boosted my character to 90 rdm, no ventures and no levels on GC. So nothing for the advertised instant boost to level 90 rdm, still. :/

Are you able to change the job with the retainer vocate and then use the book after switching them to red mage? I've never used one of these items so I don't know how they work, but I believe you have to go to the vocate to change their job