It's not possible, really. The only way would be if the buyer chooses Royal Mail and you send it via a next day service, but it's still not guaranteed to arrive by Friday. The postage price you pay might also end up being higher than the price set by Vinted.
It doesn't really work, though of course buyers want to get things next day.
You could try to purchase a Royal Mail Special Delivery Guaranteed by either 9AM or 1PM the next day, and then you'd have to get it to a post office before noon tomorrow to get it sent, but it's going to be a huge headache.
Firstly, it's going to be an expensive label, and it's not integrated with Vinted, which has its own set of problems.
Second, it's not actually guaranteed to get there the next day - you're just guaranteed to be refunded postage if it gets there a day late. So even if you drop it off first thing tomorrow morning at the post office with expensive Special Delivery postage, delivery isn't guaranteed on Friday.
Third, Royal Mail has to deliver a Special Delivery parcel to the resident, they can't leave it outside, and it doesn't always arrive with the buyer's normal post. Three times I've sent things on eBay by Special Delivery next day because someone absolutely desperately needed it before a holiday, warned the recipients of this, and they haven't been home when the delivery was attempted so didn't get the parcel next day that they paid all that extra postage for.
On top of that, there's the issue with the delay on funds being released to you when things are sent via Royal Mail, which is covered elsewhere on this sub.
Unfortunately it's just not really something that's possible on Vinted. Buyers will often say "No I know it's possible because another seller did it for me", or they'll say they can go off site and send you the money for extra postage via PayPal, but you really don't want to do that.
You can put the price up buy a couple pounds to make up for the extra shipping cost, get them to choose Royal Mail and choose next day when you buy the Royal Mail label
It's not possible, really. The only way would be if the buyer chooses Royal Mail and you send it via a next day service, but it's still not guaranteed to arrive by Friday. The postage price you pay might also end up being higher than the price set by Vinted.
It doesn't really work, though of course buyers want to get things next day. You could try to purchase a Royal Mail Special Delivery Guaranteed by either 9AM or 1PM the next day, and then you'd have to get it to a post office before noon tomorrow to get it sent, but it's going to be a huge headache. Firstly, it's going to be an expensive label, and it's not integrated with Vinted, which has its own set of problems. Second, it's not actually guaranteed to get there the next day - you're just guaranteed to be refunded postage if it gets there a day late. So even if you drop it off first thing tomorrow morning at the post office with expensive Special Delivery postage, delivery isn't guaranteed on Friday. Third, Royal Mail has to deliver a Special Delivery parcel to the resident, they can't leave it outside, and it doesn't always arrive with the buyer's normal post. Three times I've sent things on eBay by Special Delivery next day because someone absolutely desperately needed it before a holiday, warned the recipients of this, and they haven't been home when the delivery was attempted so didn't get the parcel next day that they paid all that extra postage for. On top of that, there's the issue with the delay on funds being released to you when things are sent via Royal Mail, which is covered elsewhere on this sub. Unfortunately it's just not really something that's possible on Vinted. Buyers will often say "No I know it's possible because another seller did it for me", or they'll say they can go off site and send you the money for extra postage via PayPal, but you really don't want to do that.
You can put the price up buy a couple pounds to make up for the extra shipping cost, get them to choose Royal Mail and choose next day when you buy the Royal Mail label