Resuarce packs for Realm?

make sure that you have the realms pack installed

I'm Samy an independent advisor. Welcome to the community. How are you?

I believe this answers your question, mate.

Can I host my Realms Plus worlds, texture packs, skins, and mash-ups on my Realm?

Yes. You can upload any worlds, texture packs, skins, and mash-ups from the Realms Plus catalog or your purchases from the Minecraft Marketplace to your Realm and invite your friends to join for free.  

With a 10-Player Realm (Realms Plus) subscription, you get all of the benefits of a Realms subscription and can also:

Play online with up to 10 friends simultaneously
Access a catalog of more than 150 marketplace packs that rotates monthly to provide fresh content

https://www.minecraft.net/realms/how-buy-realm

If you're having trouble accepting invites or joining Realms, be sure that you are not using a modded game client, and are not using a resource pack that does not contain textures for the Realm buttons. If you are, switch to the standard Minecraft
game client, click Options, click Resource Packs, then return to the default.

Thank you for the reply Jasmine,

This texture pack is on my child's account, I can PM you details if needed. Some other relevant information that may assist in a solution:

• The texture pack says "owned" in the Minecraft Store Page
• The realm is paid from that account
• The texture pack has worked on the Realm previously (until now), since the realm was started by the child account

Having checked the link you provided, I actually don't see the texture pack on either my or my child's account, that's odd, surely it has to be somewhere?

Thanks Again,

H.D.Tony