Under certain circumstances, a darkened map, or 'negative' Street View image, watermarked with the text "for development purposes only", may be displayed. This behavior typically indicates issues with either an API key or billing. In order to use Google Maps Platform products, billing must be enabled on your account, and all requests must include a valid API key. The following flow will help you troubleshoot the issue."
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It must be something to do with not having a Google API key.
I know how to get hold of one but don't know where I would put the long alphanumerical code in TribalPages once I had it!