This is Meta's primary anti-spam/anti-scam defense. New Business Manager accounts, new personal profiles, and new ad accounts are all seen as potential risk factors. The system wants you to build trust slowly.
You don't need a new ad account: You aren't trying to create a new ad account, but the process of fully integrating WhatsApp for advertising (especially for click-to-WhatsApp ads) requires assigning it as a specific advertising asset. The system is reading this action as an attempt to expand your ad capabilities too quickly.
The Trust Score: Your brand-new Business Manager has a low "trust score." You have to earn the right to manage multiple complex assets.
The Fix: You need to manually verify your business to fast-track your trust level.
Go to Meta Business Suite → Settings → Security Center.
Look for the Business Verification section.
Complete the verification process by uploading official business documents (e.g., business registration, utility bill, tax documents) that clearly show your company name and address.
Once your business is verified, this advertising limit will typically lift, and you will gain access to more ad accounts and assets.