createItemPromotion, internal server error

[tradeboxdirect]

Using below body data for createItemPromotion in sandbox env but getting error
{
"marketplaceId":"EBAY_GB",
"inventoryCriterion":{
"listingIds":[
],
"inventoryCriterionType":"INVENTORY_BY_VALUE"
},
"discountRules":[
{
"discountSpecification":{
"numberOfDiscountedItems":1,
"forEachQuantity":1
},
"ruleOrder":0,
"discountBenefit":{
"percentageOffItem":"5"
}
}
],
"name":"Buy 1 and get 2nd one 5% off -part 2",
"description":"Buy 1 and get 2nd one 5% off -part 2",
"promotionStatus":"DRAFT"
}

But getting below error

{
"errors": [
{
"errorId": 38201,
"domain": "API_MARKETING",
"category": "APPLICATION",
"message": "Internal server error encountered. If this problem persists, contact the eBay Developers Program for support."
}
]
}