eBay system't won't let me purchase First Class Mail label

[kdk8]

(I posted this last night but it is not longer here so I don't know what happened to my original post, frustrating.) Buyer selected USPS First Class Mail. Package weighs 1.5 oz in a box 12"X8"X8". eBay system won't let me buy a label for USPS First Class Mail for the amount she paid. I can't get to the original ship info I put in the listing because the web site won't let me but I'm pretty sure it is not far off from the actual weight and box size. Why would eBay allow the buyer to select USPS First Class Mail and calculate an amount but not let me purchase that label? Thanks for any help, I'm stuck. The labels I can purchase are double what buyer paid. Thanks again for any insight.

[kdk8]

Thanks again. Shipping is hard and I will always work with a buyer to try to figure out the best price if they inquire. I think I am under estimating shipping though. It’s a challenge if you don’t have it all packed up, measured and accurately weighed when listing. Who does?? 

[ms.rodriguez*]

I do. I made too many mistakes when I started.   Get a postal scale here on ebay or Amazon and have a measuring tape. Make sure you have a box to ship your item BEFORE you list.  I have a garage full of boxes and the back of my SUV.   Remember, anything more than a cubic foot (12" by 12" by 12") will have a surcharge.  Know your surcharges.   There is a surcharge for longer items.   Anyway, I rarely miss the weight .  I kinda pre-pack everything and weigh it.  Sometimes a first class box will weigh 8.3 ounces instead of 8 ounces so I pay a bit more.   I rarely sell anything big nowadays. 

I made too many mistakes when I started.  Also hunting for a box after the item sells is a big waste of time. Of course, you won't one rightaway.  So start hoarding nice boxes or order boxes.  Get a bunch of free bubblewrap from autobody shops and furniture stores.  They throw it away.  I have never spent a cent on bubblewrap or that foam paper that is fantastic. (Get that at Dollar tree.  They use it between the plates.) It's excellent for smaller items.