RAID1 is degraderad

I have a WDMYCLOUDMIRROR with serial number WUBL37243065 with two 3 TB HD WD Red type WD30EFRX. RAID1 is now degraderad and now my question is how to solve this problem.

Must I buy a new HD??
Which HD is compatible with the old one??
Are there any instruction how to do when I have change the HD to have it to work and be syncronized???
Any other info needed???

Hi @Une,

Please refer to the below link to check Raid expansion:

For more information please contact the WD Technical Support team for best assistance and troubleshooting: