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Just give the address which is shown in the request tab is enough and make sure you clicked the never expire option.
In order not to create any confusion, i wanted to add that the "never expire" option is for electum's internal accounting only... Addresses do not expire, people can still fund an address even if electrum "expired" the payment request... It's just for electrum's bookkeeping, it has nothing to do with being able to use an address or not.
I thought that it is always important to set the address to never expires before requesting the amount from sender or else it may become unspendable, but thank you for making it clear.
Just did some research about the address expire now I found that it is only for BIP70 payment protocol likely useful for the merchants.
+1, out of sMerit at the moment.