Royal Mail Shipping settings

Hi,
I would like to get big help, because I have problems with the shipping settings.
I have some single products and some other variable product in wide range variation as well.
I am using same settings for products, but on the checkout field, where must be shown the shipping methods, it doesn’t work.
With many products shown :
“There are no shipping methods available. Please ensure that your address has been entered correctly, or contact us if you need any help.”
Just one or two product showing correct information.

Please help me someone who know what is the problem.

Many thanks.

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