Meeting the subscriber and watch-hour thresholds is necessary but not sufficient \u2014 a few other things commonly block applications.
Two-Step Verification
Make sure two-step verification is enabled on your account well in advance, as this is required for monetization eligibility.
Community Guidelines Standing
Review your channel for any active strikes or policy violations, since these can block or delay your application.
Ad-Friendly Content
Check that your existing content aligns with YouTube's advertiser-friendly guidelines, since content flagged as limited or non-advertiser-friendly can affect your monetization status even after approval.