Troubleshooting · Plain-English answer
Websites block VPN IP addresses because thousands of people share them, and a few of those people spam, scrape or commit fraud. The site cannot tell you apart, so it blocks the whole address range. Switching to a different server usually gets you a cleaner address and restores access.
A VPN server's address is shared by everyone connected to it, so from a website's perspective one address generates the activity of a small town. When any of that activity looks abusive, automated defences score the address down, and services that subscribe to shared reputation lists inherit the block.
Some sites also block data centre address ranges wholesale, on the logic that residential visitors do not arrive from server farms. Nothing about this is personal, which is why the fix is changing your address rather than your behaviour.
Reconnect to a different server, since each has its own address and reputation. Clearing cookies helps when a site remembers the blocked session, and completing a CAPTCHA when offered often whitelists you for hours. For sites where you hold an account, logging in usually softens the restrictions.
If a site you pay for blocks VPNs outright, telling their support you use one for security is genuinely worth doing, since some maintain allowances for known providers. Failing that, your choice is that site without the VPN or the VPN without that site.
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