URL query string filters

Hi

following these instructions: https://docs.microsoft.com/en-us/power-bi/collaborate-share/service-url-filters I am having trouble getting this to work so I have scaled back everything to basics and am still unsuccessful. 

I am working on a report that someone else created - the table/field name is 'Product'[SKMPNO] and the criteria is a string 'BBK1'.

I started with ?filter=Product/[SKMPNO] eq 'BBK1' which then converts the spaces and other special characters to Product%2F%5BSKMPNO%5D%20eq%20%27BBK1%27.

However this is not filtering my report and I am not sure why or what else to do next as I have chosen the most basic filter I can think of.

Any advice, thoughts or pointers would be greatfully received.

Thanks

Oli