Sharing worksheets for View-Only

I have a single Pro licence and need to send URL's to various colleagues so they can view current status of project. No editing permissions are needed for these users. Am I right in thinking I should be able to do this? Everybody I have sent the link to says they are being asked to register to a free trial (not what they want nor what is needed...) Only one person is able to access and that is someone who was formerly a licenced user. Can anyone help?

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