Rateplanid in RatePlanChargeTier object
Below is from KC on rateplanchargetier,
"Prices are always stored in rate plan charge tiers even when the charge model isn't tiered pricing. You can query for Price from a RatePlanCharge object unless the charge model is volume or tiered pricing. If the charged model is volume or tiered pricing, then you need to query for Price from the relevant RatePlanChargeTier"
Rateplanid field isnt part of rateplanchargetier object. RatePlanChargeid is present but for the charge models like volume or tiered pricing RatePlanChargeid will be null. In that case how to pull fields from rateplanchargetier for a specific rateplan