Calculation error in "Introduction to Bayesian A/B Testing"?

[AhmetZamanis]

Notebook title: Introduction to Bayesian A/B Testing
Notebook url: https://github.com/pymc-devs/pymc-examples/blob/main/examples/causal_inference/bayesian_ab_testing_introduction.ipynb

Issue description

The modeling example under the subtitle Value Conversions models the revenue generated for each visitor as:
revenue = probability of paying at all * mean amount spent when paying.

The following priors are specified for the probability of purchase, theta, & mean purchase amount, lam, spent respectively:

Then, the following deterministic equation is used to calculate the average revenue per visitor, mu:

The calculation in the code:

Expected output

Shouldn't the calculation be mu = theta * lam, instead of mu = theta * (1 / lam)? Or am I missing something about the model specification?

[AhmetZamanis]

My mistake, it stems from the model specification indeed:
lam in the model is the rate parameter for an Exponential distribution, so 1/lam is the mean.