I've only tested this in the sandbox environment endpoint (https://wwwcie.ups.com/api/rating/v2409/rate)
Including the object
"SimpleRate": {
"Description": "SimpleRateDescription",
"Code": "XS"
},
Invokes the UPS Flat Rate logic and ignores the weight in favor of the package volume.
Flat Rate Codes are as Follows:
XS - Extra Small 1 - 100 cubic inches (Weight in response is 0.7)
S - Small 101 - 250 cubic inches (Weight in response is 1.8)
M - Medium 251 - 650 cubic inches (Weight in response is 4.7)
L - Large 651 - 1050 cubic inches (Weight in response is 7.6)
XL - Extra Large 1051 - 1728 cubic inches (Weight in response is 12.4)
Omit the "SimpleRate" object to fall back to package weight.
PS. The UPS API Doesn't calc the "Dimension" object to determine the package volume and determine the appropriate Flat rate code. That's up to the calling application.
First time poster long time fan.