VM's Status unauthorized in WHMCS:
Missing custom fields entries in WHMCS.
As described in SolusVM documentation custom fields are mandatory. Configure them my following the steps in the documentation or using the following article as a reference: How to create a product in WHMCS with solusvmpro module?
For new VPS, WHMCS, it will fetch the veserverid after that.
For existing VM's, it is required to update the vserverid in WHMCS from SolusVM.
Also, make sure the Hash function is configured on the edit servers page, see step 9 from How to install and configure WHMCS solusvmpro module?